This invention relates to a simplified one-step process for the preparation of polyamines containing primary amino groups.
It is known that aromatic isocyanates can be converted into primary aromatic amines by acid hydrolysis.
However, the amine resulting from this hydrolysis reacts with as yet unreacted isocyanate to form the corresponding urea thereby decreasing the amount of product amine. This secondary reaction cannot be suppressed even by using an excess of strong mineral acids. A recent example of this procedure is described in JP-P 55 007 829.
It is also known that isocyanates can be converted into amines by an acid or alkaline catalyzed reaction, as disclosed, for example, in N. V. Sidgwick, The Organic Chemistry of Nitrogen, Clarendon Press, Oxford, page 236 (1966) and in J. March, Advanced Organic Chemistry; Reactions, Mechanisms and Structure, McGraw-Hill Book Co., New York, page 658 (1968). Sidgwick indicates that isocyanate groups can be hydrolyzed under alkaline conditions but no details of such a process are disclosed. J. March also speaks in general terms of the fact that the hydrolysis of isocyanates and isothiocyanates to amines can be catalyzed with acids and bases. The occurrence of isocyanates as intermediate products is also known to those skilled in the art. For example, isocyanates are obtained in the course of the Curtius or Lossen degradation of acid azides and hydroxamic acids and are decomposed with aqueous acids to form amine salts. A procedure of this kind has been described, for example, in Organic Synthesis, Coll. Vol. IV, 819 (1963) in which the preparation of putrescine, hydrochloride is used as an example.
E. Mohr, J. prakt. Chem., 71 133 (1905) was one of the first to observe that phenyl isocyanate is more rapidly attached by dilute sodium hydroxide solution than by water at low temperatures. C. Naegeli et al., Helv. Chim. Acta, 21, 1100 (1938) report that when phenyl isocyanates substituted with electron acceptors (such as nitro groups, halogen atoms or acyl groups) are hydrolyzed in moist ether or in acetone containing 1% of water in the absence of acids or bases, the corresponding monoamines are obtained in the course of a reaction lasting from several minutes to up to one hour. From 2,4-dinitrophenyl isocyanate the amine can even be obtained in hot water without solvent in a virtually 100% yield and without side reactions leading to urea formation.
In a process for preparation of specified primary aromatic amines containing polyalkylene glycol ether segments described in DE-B 1,270,046, products obtained by the reaction of aromatic di- or triisocyanates with polyalkylene glycol ethers and/or polyalkylene glycol thioethers (preferably those with molecular weights of from 400 to 4000) are reacted with secondary or tertiary carbinols and then subjected (optionally in the presence of acid catalysts) to thermal decomposition at high temperatures in an inert solvent. One disadvantage of this process, apart from the high decomposition temperature, is that combustible, readily volatile alkenes which are explosive when mixed with air are formed in the course of thermal decomposition so that appropriate safety measures are required.
DE-B 1,694,152 (believed to correspond to U.S. Pat. No. 3,525,871) relates to the preparations of prepolymers containing at least two amino end groups by the reaction of hydrazine, aminophenylethylamine or other diamines with an isocyanate prepolymer obtained from a polyether polyol and polyisocyanate (NCO/NH ratio=1:1.5 to 1:5). Any unreacted amine must be carefully removed in a subsequent step of the process because the amine is a powerful catalyst in the reaction with polyisocyanates and shortens processing times, and may even act as a reaction component. A similar process is described in U.S. Pat. No. 3,931,116.
Another method for synthesizing polyamines containing urethane groups is described in FR-P 1,415,317 (believed to correspond to U.S. Pat. No. 3,385,829). In this process, isocyanate prepolymers containing urethane groups are reacted with formic acid to yield N-formyl derivatives which are saponified to aromatic amines having amino end groups. The reaction of isocyanate prepolymers with sulphamic acid according to DE-P 1,115,907 also leads to compounds containing amino end groups. Relatively high molecular weight prepolymers containing aliphatic secondary and primary amino groups may be obtained according to De-B 1,215,373 by the reaction of relatively high molecular weight hydroxyl compounds with ammonia in the presence of catalysts under pressure at elevated temperatures. According to U.S. Pat. No. 3,044,989 high molecular weight amines may be obtained by the reaction of relatively high molecular weight polyhydroxyl compounds with acylonitrile followed by catalytic hydrogenation. Relatively high molecular weight compounds containing amino end groups and urethane end groups may also be obtained according to DE-A 2,546,536 (believed to correspond to U.S. Pat. No. 4,224,417) and U.S. Pat. No. 3,865,791 by the reaction of isocyanate prepolymers with enamines, aldimines or ketimines containing hydroxyl groups, followed by hydrolysis. Another method for the synthesis of aromatic polyamines containing urethane and ether groups is opening of the ring which occurs in the reaction of isatoic acid anhydride with diols. Polyamines of this kind have been described, for example, in U.S. Pat. No. 4,180,644 and DE-A 2,019,432, (believed to correspond to U.S. Pat. No. 3,808,250) 2,619,840, (believed to correspond to U.S. Pat. Nos. 4,169,206 and 4,260,557), 2,648,774 (believed to correspond to U.S. Pat. Nos. 4,129,741 and 4,247,677), and 2,648,825 (believed to correspond to U.S. Pat. No. 4,153,801). Aromatic ester amines obtained by such methods have the disadvantage of being insufficiently reactive for many purposes.
Low reactivity is also found in compounds containing amino and ester groups obtained according to U.S. Pat. No. 4,504,648 by the reaction of polyether polyols with p-aminobenzoic acid ethyl ester and according to EP 32,547 (believed to correspond to U.S. Pat. No. 4,328,322) by the reaction of polyols with nitrobenzoic acid chloride followed by reaction of the nitro groups to amino groups.
The reaction of nitroaryl isocyanates with polyols followed by reduction of the nitro group to aromatic amine groups is also known (U.S. Pat. No. 2,888,439). The main disadvantage of this process is the high cost of the reduction stage of the process.
It is also known that certain heteroaromatic isocyanic acid esters can be converted into heteroaromatic amines by basic hydrolysis. The conditions for hydrolysis disclosed by H. John in J. Prakt, Chemie 130, 314 et seq and 3323 et seq (1931) for two quite specific heteroaromatic monoisocyanic acid esters are, however, both completely unsuitable for the conversion of polyisocyanate compounds into aliphatic and/or aromatic amines and dangerous.
Applicants' own processes disclosed in DE-A 2,948,419 and 3,039,600 (believed to correspond to U.S. Pat. No. 4,386,218) are multistage processes for the preparation of polyamines by alkaline hydrolysis of isocyanate prepolymers using an excess of base (alkali metal hydroxides) at low temperatures to form carbamates, acidification with equivalent or excess quantities of mineral acids or acid ion exchanger resins accompanied by carbamate decomposition, and optionally neutralization of excess quantities of acid by means of bases, followed by isolation of the polyamines.
DE-OS 3,131,252 (believed to correspond to U.S. Pat. No. 4,540,720) discloses a process in which the carbamates obtained in a first stage by hydrolysis with alkali metal hydroxides are decomposed by subsequent heat treatment to yield the polyamines.
One-step processes for the production of polyamines are described in DE-OS 3,223,400 (EP-97,299), (believed to correspond to U.S. Pat. No. 4,970,342) DE-OS 3,233,398 (EP-97,298; believed to correspond to U.S. Pat. No. 4,565,645) and DE-OS 3,233,397 (EP-97,290) (believed to correspond to U.S. Pat. No. 4,515,923). In these one-step hydrolysis processes various solvent-catalyst combinations are employed. "Ether solvents" are used together with tertiary amines as catalysts in DE-OS 3,223,400 (believed to correspond to U.S. Pat. No. 4,970,342). Polar solvents such as dimethylformamide are used together with tertiary amines or relatively large quantities of alkali metal hydroxides, alkali metal silicates or alkali metal cyanides as catalysts in specified amounts in DE-OS 3,233,398 (believed to correspond to U.S. Pat. No. 4,515,923). Carbonates or carboxylates are used in specified amounts in polar solvents such as DMF in DE-OS 3,233,397 (believed to correspond to U.S. Pat. No. 4,565,645.
All of these processes for the preparation of polyamines are elaborate and expensive. Even in the last mentioned, more simplified methods for the conversion of polyisocyanates to polyamines, further simplification would be desirable for obtaining polyamines even more economically with even better conversion rates of NCO/NH.sub.2 (i.e. higher NH.sub.2 numbers) by an even smoother reaction. A satisfactory process should have the following advantages compared with conventional processes:
(1) no filtration required; PA1 (2) no separation of a tertiary amine catalyst by distillation required; PA1 (3) drastic reduction in the quantity of catalyst (both tertiary amines (according to DE-OS 3,223,398) and the inorganic, alkaline compounds such as KOH) required so that the catalyst could be left in the polyamine; and PA1 (4) quantitative conversion of NCO into NH.sub.2 groups (high NCO/NH conversion rates, i.e. high amine numbers close to the theoretical value); PA1 (5) no removal of by-products required; and PA1 (6) simple working up of polyamines and auxiliary substances.